Live cell imaging of the cancer-related transcription factor RUNX2 during mitotic progression.

The nuclear matrix bound transcription factor RUNX2 is a lineage-specific developmental regulator that is linked to cancer. We have previously shown that RUNX2 controls transcription of both RNA polymerase II genes and RNA polymerase I-dependent ribosomal RNA genes. RUNX2 is epigenetically retained through mitosis on both classes of target genes in condensed chromosomes.

Subnuclear localization and intranuclear trafficking of transcription factors.

Nuclear microenvironments are architecturally organized subnuclear sites where the regulatory machinery for gene expression, replication, and repair resides. This compartmentalization is necessary to attain required stoichiometry for organization and assembly of regulatory complexes for combinatorial control. Combined and methodical application of molecular, cellular, biochemical, and in vivo genetic approaches is required to fully understand complexities of biological control.

In situ nuclear organization of regulatory machinery.

Regulatory machinery for gene expression, replication, and repair are architecturally organized in nuclear microenvironments. This compartmentalization provides threshold concentrations of macromolecules for the organization and assembly of regulatory complexes for combinatorial control. A mechanistic under standing of biological control requires the combined application of molecular, cellular, biochemical, and in vivo genetic approaches.

Microtubule-dependent nuclear-cytoplasmic shuttling of Runx2.

RUNX/AML transcription factors are critical regulators of cell growth and differentiation in multiple lineages and have been linked to human cancers including acute myelogenous leukemia (RUNX1), as well as breast (RUNX2) and gastric cancers (RUNX3). RUNX proteins are targeted to gene regulatory micro-environments within the nucleus via a specific subnuclear targeting signal. However, the dynamics of RUNX distribution and compartmentalization between the cytoplasm and nucleus is minimally understood.

Runx2 control of organization, assembly and activity of the regulatory machinery for skeletal gene expression.

We present an overview of Runx involvement in regulatory mechanisms that are requisite for fidelity of bone cell growth and differentiation, as well as for skeletal homeostasis and the structural and functional integrity of skeletal tissue. Runx-mediated control is addressed from the perspective of support for biological parameters of skeletal gene expression. We review recent findings that are consistent with an active role for Runx proteins as scaffolds for integration, organization and combinatorial assembly of nucleic acids and regulatory factors within the three-dimensional context of nuclear architecture.

Mitotic partitioning and selective reorganization of tissue-specific transcription factors in progeny cells.

Postmitotic gene expression requires restoration of nuclear organization and assembly of regulatory complexes. The hematopoietic and osteogenic Runx (Cbfa/AML) transcription factors are punctately organized in the interphase nucleus and provide a model for understanding the subnuclear organization of tissue-specific regulatory proteins after mitosis. Here we have used quantitative in situ immunofluorescence microscopy and quantitative image analysis to show that Runx factors undergo progressive changes in cellular localization during mitosis while retaining a punctate distribution.

Linkages of nuclear architecture to biological and pathological control of gene expression.

Functional interrelationships between components of nuclear architecture and control of gene expression are becoming increasingly evident. There is growing appreciation that multiple levels of nuclear organization integrate the regulatory cues that support activation and suppression of genes as well as the processing of gene transcripts. The linear organization of genes and promoter elements provide the potential for responsiveness to physiological regulatory signals.